National Institute on Aging (NIA) funded research programs using rodents to model aging processes and age-related diseases in humans require animals of defmed genotype and controlled environmental and health status. Only with the meticulous, long-term control of genetic and environmental variables is it possible to maintain relevant animal models that may be used to study manyofthe biological and behavioral processes in aging. Therefore,a continuous supply of genetically defmed, well characterized inbred and hybrid laboratory animals is essential for a program of research on aging. The purpose of this project is to develop, maintain and distribute a standing colony of aged BN and F344BN FI rats for usc by investigators in studies ofaging.